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Leibniz: An Experimental Philosopher?

In an essay that he published anonymously, Newton used the distinction between experimental and speculative philosophy to attack Leibniz. Newton wrote: “The Philosophy which Mr. Newton in his Principles and Optiques has pursued is Experimental.” Newton went on claiming that Leibniz, instead, “is taken up with Hypotheses, and propounds them, not to be examined by experiments, but to be believed without Examination.”

Leibniz did not accept being classed as a speculative armchair philosopher. He retorted: “I am strongly in favour of the experimental philosophy, but M. Newton is departing very far from it”.

In this post, I will discuss what Leibniz’s professed sympathy for experimental philosophy amounts to. Was Newton right in depicting him as a foe of experimental philosophy?

To answer this question, let us consider four typical features of early modern experimental philosophers:

self-descriptions: experimental philosophers typically called themselves such. At the very least, they professed their sympathy towards experimental philosophy.

friends and foes: experimental philosophers saw themselves as part of a tradition whose “patriarch” was Bacon and whose sworn enemy was Cartesian natural philosophy.

method:experimental philosophers put forward a two-stage model of natural philosophical inquiry: first, collect data by means of experiments and observations; second, build theories on the basis of them. In general, experimental philosophers emphasized the a posteriori origins of our knowledge of nature and they were wary of a priori reasonings.

rhetoric: in the jargon of experimental philosophers, the terms “experiments” and “observations” are good, “hypotheses” and “speculations” are bad. They were often described as fictions, romances, or castles in the air.

Did Leibniz have the four typical features of experimental philosophers?

First, he declared his sympathy for experimental philosophy in passage quoted at the beginning of this post.

Second, Leibniz had the same friends and foes of experimental philosophers. He praised Bacon for ably introducing “the art of experimenting”. Speaking of Robert Boyle’s air pump experiments, he called him “the highest of men”. He also criticized Descartes in the same terms as British philosophers:

if Descartes had relied less on his imaginary hypotheses and had been more attached to experience, I believe that his physics would have been worth following […] (Letter to C. Philipp, 1679)

Third, the natural-philosophical method of the mature Leibniz displays many affinities with the method of experimental philosophers. To know nature, a “catalogue of experiments is to be compiled” [source]. We must write Baconian natural histories. Then we should “infer a maximum from experience before giving ourselves a freer way to hypotheses” (letter to P.A. Michelotti, 1715). This sounds like the two-stage method that experimental philosophers advocated: first, collect data; second, theorize on the basis of the data.

Fourth, Leibniz embraces the rhetoric of experimental philosophers, but only in part. He places great importance on experiments and observations. However, he does not criticize hypotheses, speculations, or demonstrative reasonings from first principles as such. This is because demonstrative, a priori reasonings play an important role in Leibniz’s natural philosophy.

Leibniz thinks that we can prove some general truths about the natural world a priori: for instance, the non-existence of atoms and the law of equality of cause and effect. More importantly, a priori reasonings are necessary to justify our inductive practices.

When experimental natural philosophers make inductions, they presuppose the truth of certain principles, like the principle of the uniformity of nature: “if the cause is the same or similar in all cases, the effect will be the same or similar in all”. Why should we take this and similar principles to be true? Leibniz notes:

[I]f these helping propositions, too, were derived from induction, they would need new helping propositions, and so on to infinity, and moral certainty would never be attained. [source]

There is the danger of an infinite regress. Leibniz avoided it by claiming that the assumption of the uniformity of nature is warranted by a priori arguments. These prove that the world God created obeys to simple and uniform natural laws.

In conclusion, Leibniz really was, as he wrote, “strongly in favour of the experimental philosophy”. However, he aimed to combine it with a set of a priori, speculative reasonings. These enable us to prove some truths on the constitution of the natural world and justify our inductive practices. Leibniz’s reflections are best seen not as examples of experimental or speculative natural philosophy, but as eclectic attempts to combine the best features of both approaches. In his own words, Leibniz intended “to unite in a happy wedding theoreticians and observers so as to improve on incomplete and particular elements of knowledge” (Grundriss eines Bedenckens […], 1669-1670).

2 thoughts on “Leibniz: An Experimental Philosopher?”

This result—Leibniz too is experimental!—makes me wonder whether the distinction between experimental and speculative doesn’t distinguish philosophical styles better than it does philosophers. After all, if you except #2 above (for the obvious reason), Descartes comes out as experimental too.

Furthermore (and with John Schuster’s “debunking” of method talk in mind), once it becomes apparent that being, or at least presenting oneself as being, experimental will be regarded as a positive quality in the discursive arena of natural philosophy, then the attribution to oneself of the characteristics of an experimental philosopher may sometimes be a mere device, like (as Schuster argues) the attribution to oneself of adherence to a method.

So it is worth considering whether, as the new philosophy matures, “experimental” (in its contrast with “speculative”) doesn’t denote rather a style that like other styles one may take up without a strong commitment to the underlying substance (e.g. to the actual collecting of data and performing of experiments).

Many thanks for the suggestion. I agree that the experimental-speculative distinction is, among other things, a distinction between different styles, rhetorics, or method-talks. The question is whether the experimental-philosophical distinction was only a distinction between styles, rhetorics, and method-talks.

It seems to me that there is a substantive, and not merely rhetorical, difference between the experimental natural philosophy of Boyle, Hooke, Locke, and Newton on the one hand, and the natural philosophy of Descartes, Leibniz, and Wolff on the other. Experimental natural philosophers rejected a priori arguments and demonstrative reasonings in favour of a posteriori arguments based on experiments and observations. By contrast, the natural philosophy of Descartes, Leibniz, or Wolff is based on a priori arguments, as well as experiments and observations. Typically, for these authors, a priori arguments provide knowledge of the basic structure of the natural world and of some laws governing it. Experimental philosophers like Boyle and Hooke thought that we will be able to achieve this knowledge only a posteriori, in a distant future, after collecting and organizing a large amount of empirical data into natural histories.

Would you agree that this is a substantive and not merely stylistic difference between experimental natural philosophers on the one hand, Descartes and Leibniz on the other?

Incidentally, Leibniz did not call himself an experimental philosopher. He only said that he was in favour of experimental philosophy. This seems to me to be consistent with his attempt to overcome what he took to be the limits of the experimental approach with a priori reasonings.

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